1. Field of the Invention
The present invention relates to a channel card for extending the coverage area of a base station. Specifically, the invention relates to a channel card for extending the coverage area of a base station, which controls global positioning system (GPS) reference signals provided to base station modems to extend the coverage area by up to four times a general base station coverage area.
2. Description of the Related Art
The base station of a mobile communication system such as a digital cellular system (DCS) and personal communication system (PCS) generally includes a channel card handling actual calls. This channel card determines the coverage area of the base station on the basis of the modem of the base station. FIG. 1 shows a conventional base station channel card.
Referring to FIG. 1, a high level data link control (HDLC) unit 1 transmits/receives data to/from a control station, and a CPU 2 controls the entire operation of the base station system. A memory 3 is connected to the HDLC unit 1 and a controller 5 to store control data and generation data. A GPS clock receiver 4 receives clocks sent from a GPS and transmits it to a base station modem 6 which will be described below. The controller 5 is connected to the CPU 2, HDLC unit 1, memory 3 and base station modem 6 to control all devices of the channel card under the control of the CPU 2. The base station modem 6 taking charge of calls is controlled by the controller 5 and operates by a reference clock transmitted from the GPS clock receiver 4. A data receiver 10 receives data sent from a mobile through an intermediate frequency (IF) demodulator and transmits the data to the base station modem 6. Further, a serial-parallel converter 7 converts serial data which has passed through the base station modem 6 and controller 5 into parallel data. This parallel data is converted into analog data by a D/A converter 8. A data transmitter 9 delivers this analog data to an IF modulator to transmit it to the mobile.
The conventional channel card constructed as above is used for a general base station to cover only regions having the radius of 60 Km. Accordingly, a base station whose coverage area is extended to 120 Km, 180 Km or 240 Km that is twice, three times or four times the 60 Km has to develop and employ a new channel card for extension of its coverage area. That is, the channel card used for the general base station cannot be used for the base station whose coverage area is extended. This requires development of a new channel card for extension of the coverage area. Furthermore, base stations having different coverage areas need different channel cards suitable for their coverage areas, resulting in increase in development costs.
It is, therefore, an object of the present invention to provide a channel card for extending the coverage area of a base station, which controls GPS reference signals provided to the modem of the base station to extend the coverage area of the base station by up to four times a general coverage area, being capable of being commonly used for base stations having extended coverage areas as well as the general base station.
To accomplish the object of the present invention, there is provided a channel card for extending the coverage area of a base station, which includes: a controller for generating control signals for extending the coverage area of the base station;
a system clock distributor for dividing a GPS reference signal applied from a GPS clock receiver to generate a plurality of system clocks; a coverage area extending clock generator for converting the GPS reference signal supplied from the GPS clock receiver into a plurality of signals under the control of the controller, to generate clocks for extending the coverage area; a coverage area extending clock controller for selectively providing the plurality of coverage area extending clocks generated by the coverage area extending clock generator to first to fourth base station modems under the control of the controller; and the first to fourth base station modems which operate according to the coverage area controlling clocks provided by the extending clock controller and the system clocks generated by the system clock distributor, to handle calls established in a first area having the minimum coverage area to a fourth area having the maximum coverage area.